40 lines
1.1 KiB
JavaScript
40 lines
1.1 KiB
JavaScript
var BITMASK = [0, 0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F, 0xFF];
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// returns a function that reads bits.
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// takes a buffer iterator as input
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module.exports = function bitIterator(nextBuffer) {
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var bit = 0, byte = 0;
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var bytes = nextBuffer();
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var f = function(n) {
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if (n === null && bit != 0) { // align to byte boundary
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bit = 0
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byte++;
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return;
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}
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var result = 0;
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while(n > 0) {
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if (byte >= bytes.length) {
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byte = 0;
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bytes = nextBuffer();
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}
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var left = 8 - bit;
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if (bit === 0 && n > 0)
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f.bytesRead++;
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if (n >= left) {
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result <<= left;
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result |= (BITMASK[left] & bytes[byte++]);
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bit = 0;
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n -= left;
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} else {
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result <<= n;
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result |= ((bytes[byte] & (BITMASK[n] << (8 - n - bit))) >> (8 - n - bit));
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bit += n;
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n = 0;
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}
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}
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return result;
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};
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f.bytesRead = 0;
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return f;
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};
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